Polyvinyl chloride (PVC) is presently used in myriad useful applications; some such applications involve the introduction of hot substances into containers molded from a PVC composition. Conventional PVC compositions contain additives such as liquid epoxy type stabilizers (e.g. epoxidized soybean oil). These stabilizers, when blended into the PVC resin, have a tendency to reduce the glass transition temperature (Tg) of the PVC compound; thus decreasing the softening temperature of the processed PVC product. This decrease in softening temperature leads to problems where hot substances are introduced into PVC products such as bottles; the bottles tend to sag and distort.
The instant invention overcomes these problems by blending with PVC, an epoxy type stabilizer system that results in a PVC composition with a Tg equal to or greater than the Tg for the PVC composition without the epoxy type stabilizer. More specifically, the instant invention teaches blending with PVC either a copolymer of an .alpha.-olefin and at least one unsaturated epoxy monomer or optionally blending with PVC a terpolymer comprised of the aforementioned copolymer plus an epoxy-free monomer wherein the epoxy-free monomer can also be an .alpha.-olefin.
Copolymers of unsaturated epoxy monomers and ethylene have been long known in the art. For example, U.S. Pat. No. 3,383,372 (Spivey) discloses a copolymer comprised of ethylene and glycidyl esters such as glycidyl acrylate, glycidyl methacrylate and glycidyl ethacrylate. These copolymers, as taught by Spivey, are either used alone or are modified with fillers and plasticizers as molding compositions for the manufacture of films and coating.
Another reference to copolymers of unsaturated epoxy monomers is found in U.S. Pat. No. 3,201,497 (Heino). This reference relates to epoxy resin adhesive compositions comprised of an epoxy resin, a copolymer of an ethylenically unsaturated epoxy monomer and an ethylenically unsaturated epoxy-free monomer and a curing agent for the epoxy resin.